Laura Barton on extreme sports

It took her five hours and two minutes, running uphill and down and through temperatures ranging from -20C to 20C, but Angela Mudge, 37, has broken the women's record for the Everest Marathon by 13 minutes. She was sustained, she said, by jelly beans, and by thoughts of her twin sister, Janice, also an accomplished runner, who died from bowel cancer aged just 35.

The Everest Marathon is gruelling before it even begins. Even on the trek to the starting line - at 5,200 metres - most of the 84 competitors suffered altitude sickness, diarrhoea, deep-vein thrombosis, reduced lung capacity or chest infections.

Mountain running is one of a number of increasingly popular extreme sports that require a mixture of skill and sheer swarthy endurance to succeed. Take adventure racing, which includes trail running, mountain biking and paddling, and sometimes paragliding, camel-riding, roller-skating and swimming to boot.

With their increased popularity has come a dramatic increase in sponsorship and coverage on extreme sports TV channels. Many activities, such as sky-running, sky-skiing and sky-biking, are conducted at high altitude; others take place on ice, in mid-air, or underwater, such as free-diving, which is an attempt to reach certain depths, times or distances without breathing apparatus.

"It's proving oneself privately and personally," says Dr Amanda Williams, a psychologist at UCL, and herself a free-diver. "Some people are more into risk-taking. It's just taking something that is normally a pleasure to a much more passionate level."

Another attraction of sports such as free-diving and mountain running may be their spirit of exploration. Williams speaks, for example, or interacting with sea creatures while free-diving. "It makes you feel more part of the world," she says. "And I know hang-gliders often feel affinity with large birds of prey." The experience itself, she says, is unparalleled: "Free-diving gives you a completely amazing high - though not necessarily at the time. It's like flying in dreams. There is a sense of energy and grace you don't get elsewhere."